This invention relates to anti-fouling devices for watercraft, and particularly, to a self-powered anti-fouling device. It is known that watercraft can be protected against fouling, that is, the growth thereon of water dwelling organisms, by causing the craft hull to vibrate continuously at some audio frequency, e.g., 20 KHz. One means to accomplish this is disclosed by Latour and Murphy, "Application of PVF.sub.2 Transducers As Piezoelectric Vibrators for Marine Fouling Prevention", Ferroelectrics, 1981, Vol. 32, Pages 33-37. Their article comprises disposing an electroded thin layer of a piezoelectric plastic material on a boat hull at and below the water line and applying an a.c. voltage at the desired frequency between the layer electrodes. Applying a voltage across a piezoelectric material causes a deformation or straining of the material, and applying an a.c. voltage across the material causes it to vibrate at the frequency of the applied voltage.
The piezoelectric plastic layer can be bonded to or embedded within the hull of a watercraft and, once in place, can be used indefinitely. A problem, however, particularly with small watercraft, is the need to provide electrical power for driving the piezoelectric vibrator. On small craft, even small engines for trickle charging a battery are generally undesirable, hence a need exists for an arrangement, particularly suitable for use in small watercraft, for trickle charging a battery used for supplying energy to the piezoelectric vibrator.